The last decade has witnessed the expanding use of handheld electronic devices. Although handheld devices are easily carried, they rely on power from batteries and further from power supplying devices in case the battery power is exhausted. The charging of handheld electronic devices is completed through a transformer or voltage converter that must comply with specific requirements since the charging voltage is designed as being fixed for a charger and cannot be adapted to different electronic devices.
As the number and types of personal handheld electronic devices increase, the charging requirements and specifications are not unified among different electronic devices. To address the need to charge different electronic devices, one should prepare multiple transformers or voltage converters with different charging standards. Thus, it is desired to improve existing transformers or voltage converters in order to meet the charging requirement of handheld electronic devices.